Tear resistant heat sealable packaging structure

ABSTRACT

A tear resistant laminated paperboard product comprised of a polyolefin tie layer, a tear resistant layer, and a heat-sealable polymer material.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

[0001] The present invention relates to a flexible, multi-layer paperboard structure that may be heat sealed to form a tear resistant packaging material. This tear resistant structure is composed of at least one layer of a tear resistant material in addition to a flexible coating comprised of a low-density polyolefin and a heat-sealable polymer material. The laminated structure is suitable for packaging applications where extra security or child resistance is favored.

BACKGROUND OF THE INVENTION

[0002] Use of heat sealable paperboard materials for packaging is described, for example, in U.S. Pat. No. 5,091,261 (Casey et al.). This patent describes a laminate for packaging applications comprised of a paperboard substrate having one coated, printable surface (C1S), and having adhered to the opposing side a co-extrudate of low density polyethylene and an adhesive material, for example, ethylene methyl-acrylate copolymer. This adhesive material enables the laminate to be used for applications such as the manufacture of blister cards, which requires that a tight seal be formed between the laminate and the plastic material of the blister. In this regard, the adhesive material is a heat sealable component that plasticizes at low heat, so that when opposing surfaces treated with the same material are contacted, the adhesive material bonds together to form a seal.

[0003] U.S. Pat. No. 6,010,784 relates to a similar paperboard laminate, where an ethylene-vinyl acetate based hot melt forms the sealant layer, for pharmaceutical blister packaging. The hot melt layer seals to common blister forming films including polychlorotrifluoroethylene (Aclar®), a high barrier film.

[0004] The packaging laminates described in U.S. Pat. Nos. 5,091,261 and 6,010,784 exhibit the additional advantage of being clay-coated and thus printable on one side. Accordingly, they are suited to consumer packaging applications, for example, for packaging of unit dose pharmaceuticals. However, these products lacked high tear resistance and burst resistance, which are both characteristics desired for various packaging applications including but not limited to pharmaceutical packaging.

[0005] Unit dose packaging is an attractive packaging format for certain pharmaceutical applications because it is convenient, yet sturdy enough to be opened and closed numerous times until the course of medication is completed, and also enables the user to track the consumption of doses according to the prescribed schedule. Examples of such packaging are described in commonly assigned U.S. Pat. No. 6,047,829 (Johnstone). The Johnstone patent relates to a unit dose paperboard package that includes an outer paperboard sleeve, an inner paperboard slide card that is lockably retained within the sleeve. The sleeve includes a plurality of side panels operatively connected to each other such that one of said plurality of side panels includes a first inner slide card releasing means, and another of said side panels includes a second inner slide card releasing means, such that the inner slide card retaining and releasing means are located substantially adjacent to said unit dose dispensing means.

[0006] Child resistance is a feature particularly desired for unit dose pharmaceutical packaging, and is mandated by the Poison Prevention Packaging Act of 1970. Guidelines are prescribed for packaging to satisfy the criteria for child resistance under the statute. For example, a child resistance (CR) rating of F=1 requires that a random sampling of the subject packages not be compromised by an age specific test pool of children at a failure rate of greater than 10%. This general guideline is designed to ensure that the package has sufficient integrity against tampering by children.

[0007] While modifying package design provides one avenue for improving child resistance, it would also be beneficial to provide similar improved tolerance in packages having a known or more conventional design and construction. In this respect, improving tear resistance is necessarily accomplished by developing packaging materials having such characteristics. At the same time, it is preferred that such packaging material also have a heat sealing ability suited to secure packaging of consumable goods. These objectives are met by the various embodiments of the tear resistant packaging material described and claimed herein.

SUMMARY OF THE INVENTION

[0008] The present invention provides an improvement over the previously developed heat sealable packaging laminates in that there has now been developed a laminate product having structural elements that contribute a desirable flexibility while at the same time improving the product's resistance to tearing. These effects are achieved using a standard paperboard material as the substrate.

[0009] In one aspect, the invention therefore comprises a laminated structure comprised of a paperboard substrate, one or more polyolefin tie layers, one or more layers of a tear resistant material; and one or more layers of a heat seal component.

[0010] In another aspect, the invention encompasses a method of packaging an article in tear resistant packaging comprising:

[0011] a) forming a packaging blank from a tear resistant laminate composed of

[0012] i) a paper or paperboard substrate;

[0013] ii) a tear resistant layer;

[0014] iii) a polyolefin tie layer interposed between the substrate and the tear resistant layer; and

[0015] iv) a layer of heat seal component

[0016] b) folding the blank and heat sealing the exposed heat seal component at the points of contact to form a container; and

[0017] c) inserting an article within the container.

[0018] In yet another aspect, the invention comprises a method for secure packaging of consumable goods comprising:

[0019] a) forming one or more portions of a packaging container from a tear resistant laminated structure formed by:

[0020] (i) extruding a tie layer between a paperboard substrate and a tear resistant layer; and

[0021] (ii) extruding one or more layers of a heat seal component over the tear resistant layer to form a tear resistant laminated structure; and

[0022] b) optionally, printing text or graphics on the side of the paperboard substrate opposite the tear resistant layer;

[0023] c) cutting the laminated structure to form a packaging blank;

[0024] d) folding the packaging blank and heat sealing the exposed heat seal component at the points of contact to form a container; and

[0025] e) inserting a consumable good within the container interior.

[0026] The packaging may be formed around the good, for example as in a blister card; or, alternatively, the packaging may be first formed and the consumable good inserted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a schematic representation of a process for making a laminated structure using a tear resistant film and a co-extruded sealant.

[0028]FIG. 2 is a schematic representation of a process for making a laminated structure using a tear resistant film and a single sealant layer.

[0029]FIG. 3 is a schematic representation of a process for making a laminated structure using an extruded tear resistant layer and sealant layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0030] The invention provides a packaging material that is resistant to tearing or burst damage and thus provides more security to the package contents when it is used, for example, to form a folded box, envelope, blister card or other package. This feature is particularly desirable in the foldover blister packaging of pharmaceuticals where regulatory guidelines specify a certain acceptable level of child resistance. At the same time, the package must be user-friendly, fitted to frequent repeat usage and easily manipulated by the consumer.

[0031] The laminated structure of the present invention comprises one or more materials that, in combination, produce the resilience that has now been discovered.

[0032] The substrate material may be selected from any conventional paperboard grade, for example solid bleached sulfate (SBS) ranging in weight upward from about 10 pt., preferably from about 11 pt. to about 14 pt. An example of such a substrate is a 12-point SBS board manufactured by Westvaco Corporation. The substrate may also be an unbleached board, depending on the desired appearance of the final package. The board is preferably coated on at least one side, preferably the side opposite the lamination, with a conventional coating selected for compatibility with the printing method and board composition. The coated side would typically be presented on the external surface of the package to allow for printing of text or graphics.

[0033] To the uncoated side of the substrate is applied at least one layer of a tear resistant polymeric material. The tear resistant layer imparts toughness to the laminate structure. Suitable materials to be used in this capacity include n-axially oriented films, e.g. MYLAR™, which is a biaxially oriented polyester, oriented nylon, e.g. DARTEK™, cross-laminated polyolefin film, e.g. VALERON™ or INTEPLUS™, which are high density polyolefins. The orientation and cross-laminated structure of these materials contribute to the tear resistant characteristic. Also, tear resistance may be attributed to the chemical nature of the tear resistant material. An example of a chemically strengthened material is extruded metallocene-catalyzed polyethylene (mPE). A tie layer of LDPE is interposed between the paperboard layer and the tear resistant layer (FIGS. 1 & 2). Alternatively, the tear resistant layer may be an extrusion-coated layer of LLDPE or mPE (FIG. 3). In various embodiments where linear low-density polyethylene (LLDPE) or mPE is used, however, it is not necessary to incorporate an additional tie layer of LDPE. Other suitable flexible materials having a high level of tear resistance may also be used. It has now been found that various combinations of these materials in which at least one layer of the tear resistant material and the heat seal component, when applied to a bleached board substrate, produce the favored tear resistance performance.

[0034] Where a sheet material such as oriented polyester or nylon or cross-laminated is used as the tear resistant layer, a caliper ranging from about 0.75 mils (approximately 16 lb./ream) or more is preferred. As used herein, ream size≈3000 ft². For example, a suitable caliper of tear resistant material may range from about 0.75 mils or more, preferably from about 1 mil to about 5 mils. In embodiments in which the tear resistant layer is formed from a bulk polymer material that is extruded onto the substrate, the polymer melt is extruded to yield a coat weight of from about 10.8 to about 70 lb./ream, preferably 14 to about 35 lb./ream.

[0035] An additional layer of the laminate structure is formed by a polyolefin material, which acts as a tie layer and also imparts flexibility to the laminate. A preferred polyolefin for this purpose is linear low-density polyethylene. It has also been found, however, that a low-density polyethylene can be substituted without deleterious effect. The tie layer is formed between the paperboard and the tear resistant layer. It should also be noted that one or more types and/or layers of the tear resistant material, tie layer and heat seal component may be included in various embodiments of the laminated structure.

[0036] The heat seal component may be applied by a process such as melt extrusion, film coating, spraying, roll coating or other means. The heat seal component serves as an adhesive that bonds the layers of the laminate together to form a compact, tightly layered structure. Examples of the heat seal material are ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA) copolymers, or combinations thereof. Preferably, the heat seal layer is applied by melt extrusion either by co-extruding simultaneously or in tandem with the low density polyolefin tie layer at a coat weight of from about 5 to about 14 lb./ream, preferably about 8 to 10 lb./ream. The process of co-extruding the polyolefin and adhesive film layers, shown in FIG. 1, is described in detail in U.S. Pat. No. 5,091,261, the entire disclosure of which is incorporated herein by reference.

[0037] In a preferred embodiment of the invention, as shown in FIG. 1, a laminate structure is formed in an in-line operation by unwinding a C1S paperboard substrate, overlaying the substrate and simultaneously extruding a polymer melt of LDPE and tear resistant film onto one side. A layer of a heat seal component, which is a combination of LDPE and ethylene methacrylic acid (EMA), is extruded over the tear resistant substrate. According to FIG. 2, the sealant layer may be a single component, EVA. Alternatively, as shown in FIG. 3, both the tear resistant layer and the heat seal component may be co-extruded. In such an application, a chemically strengthened material such as mPE, which may be extruded without compromise to its strength characteristics, is used as the tear resistant layer.

[0038] The resulting flexible, laminated structure of the invention may be used in any packaging application where tear resistance is required. One of many such applications is the packaging of pharmaceuticals such as prescription medications. In one exemplary application, the laminate may be used to form the outer packaging of a box housing unit dose medications. In such an embodiment, the medications may be housed in individual doses on a blister card that is contained within the box interior. The box blank may be configured and folded to provide a retention means for the blister card, thereby preventing its complete withdrawal from the package interior. Such retention means are disclosed, for example, in U.S. Pat. No. 6,047,829 (Johnstone). In the alternative, the blister card may be unattached so as to allow its complete withdrawal from the package, if desired. Packaging of other articles such as dry or semi-moist foods, cosmetics, small electronics, recording media such as CDs and tapes and various other articles are also contemplated and should be viewed as falling within the scope of this disclosure. The laminate structure of the invention may, however, also be manufactured using a lighter weight paperboard substrate or even a paper, for example, envelope grade material, to manufacture other types of containers such as envelopes or mailers. The range of potential applications is therefore quite extensive for this versatile composition.

EXAMPLES Example 1

[0039] Tear resistance of several extrusion coatable polymers coated onto 61-lb. weight paper substrate were evaluated and reported in Table 1. Tear resistance was determined as grams force in the machine- and cross-directions (MD and CD, respectively). Burst strength was reported in pounds per square inch (psi).

[0040] As shown, metallocene-catalyzed polyethylene (mPE) demonstrated significantly greater tear resistance than LDPE, EMA, cross-laminated film (VALERON™), and ionomer (cationically neutralized EMA copolymer, DuPont), when coated onto the substrate. TABLE 1 Comparison of tear resistant laminates. Layer Type: 2.5 mil Substrate: Valeron ™ on 1 mil LDPE on .75 mil EMA on 1 mil ionomer on 1 mil mPE on Measurement 61 # paper Tyvek ™ 80# paper 61# paper 61# paper 61# paper 61# paper Total Caliper, 5 5.9 8.8 5.8 5.5 5.8 5.7 mils Basis Weight, 17.6 11.7 41.7 22.3 21.4 23.2 23.9 lbs/1000 sq. ft. MD Tear, 80 592 511 63 117 97 525 gm-force CD Tear, 93 622 834 67 121 103 507 gm-force Burst 36.8 113 52 40.2 37.2 37.8 35.8 Resistance, psi

Example 2

[0041] An example of tear resistant layer material was also evaluated to determine the effect of layer thickness on tear resistance and burst resistance, again by measuring tear and burst resistance as described above. In this example, mPE was used. Coatings were applied at calipers of from about 1 mil to about 5 mils (approximately 14 lb./ream to about 67.2 lb./ream coat weight, respectively). The results are reported in Table 2. TABLE 2 Effect of increasing mPE coat weight on paper 2.5 mil Valeron ™ Increasing coat weights of mPE on 61# paper 61 # paper Tyvek ™ on 80 # paper 1 mil 2 mil 2.5 mil 3 mil 4 mil 4.8 mil Total Caliper, 5 5.9 8.8 5.7 6.7 7.1 7.5 8.7 9.5 mils Basis Weight, 17.6 11.7 41.7 23.9 28.7 30.2 31.8 38.2 41.8 lbs/1000 sq. ft. MD Tear, gm- 80 592 511 525 664 734 605 976 1246 force CD Tear, 93 622 834 507 645 864 750 1108 1208 gm-force Burst 36.8 113 52 35.8 38.6 38.8 40.6 44 46.2 Resistance, psi

[0042] Table 2 indicates that mPE coated at a range of thickness from 1 mil upward provides good tear resistance.

Example 2

[0043] Laminated structures according to various embodiments of the invention are prepared according to the combinations recited in Table 3. TABLE 3 TEAR RESISTANT HEAT SEAL SUBSTRATE MATERIAL COMPONENT 12 pt. SBS Metallocene LDPE/EMA coextrusion polyethylene or EVA monolayer 12 pt. SBS Oriented polyester LDPE/EMA coextrusion or EVA monolayer 12 pt. SBS Cross-laminated film LDPE/EMA coextrusion or EVA monolayer

Example 3

[0044] The tear resistance of various structures prepared according to the invention was evaluated. Laminates were prepared by layering metallocene-catalyzed polyethylene, 2.5 mils (35 lbs./3000 ft²) or, alternatively, biaxially oriented polyester, 0.75 mils (16 lbs./3000 ft²) on 12 or 14 point SBS paperboard. The heat seal layer (Hot melt HL9918X, from H. B. Fuller) was applied by melt extrusion at a coat weight of about 9 lbs. 13000 ft². Multiple samples of equivalent dimension were subjected to the Elmendorf tear propagation resistance evaluation, the results being measured in grams-force. The samples were also tested using the Graves tear test to determine tear initiation resistance at maximum load. The results are reported in Table 4. TABLE 4 BASIS Elmendorf Tear Graves Tear CALIPER WEIGHT (grams-force) (lb/in.) SAMPLE LAMINATE COMPOSITION (Mils) (lbs./3000 ft²) MD CD MD CD C 12 pt. SBS/metallocene- 14.71 197.97 761 823 29.7 20.3 catalyzed PE D 14 pt. SBS/biaxially oriented 15.84 211.20 359 337 37.2 29.2 polyester E 14 pt. SBS/cross-laminated 18.32 233.97 1432 807 35.0 25.9 film

[0045] The tear resistance performance demonstrated in Table 4 indicate that the laminate incorporating metallocene-catalyzed polyethylene has good tear propagation resistance; the laminate incorporating biaxially oriented polyester has good tear initiation resistance; and the laminate incorporating cross-laminated film has excellent overall tear strength, showing both good tear initiation and tear propagation resistance. 

We claim:
 1. A tear resistant packaging laminate comprising: a paper or paperboard substrate; one or more polyolefin tie layers; a tear resistant layer; and one or more layers of a heat seal component.
 2. The structural laminate of claim 1 wherein the paperboard substrate is a C1S solid bleached sulfate (SBS) board.
 3. The structural laminate of claim 1 wherein the polyolefin layer is low-density polyethylene or linear low density polyethylene.
 4. The structural laminate of claim 1 wherein the tear resistant layer is selected from the group consisting of n-axially oriented polyester film, oriented nylon film, cross-laminated polyolefin film, and chemically strengthened polymer film.
 5. The structural laminate of claim 1 wherein the chemically strengthened polymer film is an extruded coating of metallocene catalyzed polyethylene.
 6. The structural laminate of claim 1 wherein the tear resistant layer is applied at a thickness of from about 1 mil up to about 5 mils.
 7. The structural laminate of claim 1 wherein the heat seal component is ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer or a combination thereof.
 8. A method of packaging a consumable good to achieve improved child resistance comprising: a) forming one or more portions of a packaging container from a tear resistant laminated structure formed by: i) layering together a paperboard substrate and a tear resistant layer; and ii) co-extruding one or more polyolefin tie layers and one or more layers of a heat seal component over the tear resistant layer to form a tear resistant laminated structure; and b) optionally, printing text or graphics on one side of the paperboard substrate opposite the tear resistant layer; c) cutting the laminated structure to form a packaging blank; d) folding the packaging blank and heat sealing the exposed heat seal component at the points of contact to form a container; and e) inserting a consumable good within the container interior.
 9. The method of claim 8 wherein the consumable good is contained in discrete compartments within the container interior.
 10. The method of claim 9 wherein the consumable good is contained on a blister card.
 11. The method of claim 9 wherein the consumable good is a unit-dose pharmaceutical.
 12. A package formed from a laminated structure comprising: a) a paper or paperboard substrate; b) one or more polyolefin tie layers; c) a tear resistant layer; and d) one or more layers of a heat seal component. 